Session Initiation Protocol (“SIP”) is an application-layer control protocol for creating, modifying, and terminating sessions with one or more users. These sessions include Internet telephone calls, multimedia distribution and multimedia conferences. SIP invitations create sessions that allow the users to agree on a set of compatible media types based on session descriptions configurable within the protocol. A SIP session with one or more users can occur over a SIP based network, such as the Internet Protocol Multimedia Subsystem (“IMS”) network.
IMS is a standardized next generation networking architecture for providing multimedia services in mobile/wireless and fixed/wire-line communication networks. IMS uses the Internet protocol (“IP”) for packet-data communications generally, and voice over IP (“VoIP”) for voice communications, based on a 3rd Generation Partnership Project (“3GPP/3GPP2”) standardized implementation of SIP. IMS includes session control, connection control, and an application services framework along with subscriber and services data. It enables the use of new converged voice and data services, while facilitating the interoperability of these converged services between subscribers. However, in a typical IMS network, there are multiple sources of subscriber data located in multiple different locations.